High and low dose radiation processing applications require a wide range of dosimetry control in order to assure that the correct dose is delivered. Dosimeters are used for measuring the exposure, kerma and absorbed dose, resulting from the interaction of ionizing radiation with matter. Radio-chromic films are one category of dosimeters which depend on permanent change in color due to a radiation-induced chemical changes. The films do not require any latent thermal, optical or chemical development or amplification (Kovács, A., et. 1999.). There are various types of radio-chromic film dosimeters. The competition between these systems depends on their accuracy, the lower and higher dose to be measured and their behavior under different environmental conditions such as dose rate, temperature, humidity, etc.
A formyl violet cyanide liquid dosimetry system (Ebraheem, S., et.al. 2002) depends on aqueous solution of formyl violet cyanide in the dose range 400-4000 Gy. This system was investigated for potential use in radiation dosimetry using both absorption and fluorescence. It was observed that the dose range depends on the concentration of the dye.
Calderon, J. M., et.al. (2007). investigated ferrous ammonium sulfate as a high dose dosimeter in the range from 30 kGy to 550 kGy with very low temperatures in the range from 77 K (liquid Nitrogen) to 300 K. The analysis of the samples was made by UV spectroscopy and EPR, it was observed that the change in absorbance of the salt to radiation was linear with respect to the absorbed dose. In this study, it is very interesting to notice the high range of irradiation and at very low temperatures.
Seito, H., et.al. (2009). conducted a study on the use of clear Perspex (poly methyl methacrylate) dosimeter and evaluated its characteristics. In his study the Radix W, commercially available un-dyed PMMA dosimeters were studied, in the dose range from 0.5 to 8.0 kGy, the characteristics of dose response, the effect of irradiation temperature and stability after irradiation were examined, and different wave lengths between 270-320 nm were used to read the absorbance. It was found that the suitable wave length is 280 nm for measuring the dose in the range from 0.5 to 8.0 kGy and the dose response is higher for higher temperature in the range of 20-40° C., and it was found that the decrease in the dosimeter dose response is less than 1% within 24 hours after irradiation. The clear PMMA dosimeter is very useful, since the range of 0.5 to 8.0 kGy is very useful in radiation processing especially in the food irradiation.
Recently, a radio-chromic film dosimeter based on polyvinyl butyral (PVB) containing 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MMT) (Basfar, A et.al. U.S. Pat. No. 8,691,135) and a radio-chromic film dosimeter based on polyvinyl butyral (PVB) containing Nitro Blue Tetrazolium (NBT) for high dose applications (Basfar, A, et.al., EP2395045). The MMT-PVB and NBT-PVB film dosimeters showed good performance for dose measurements as routine dosimeters in the dose range of 5-40 and 5-60 kGy respectively.
There is a need to find an optimal and sensitive radiochromic dosimeter that would cover the temperature, withstand humidity factors and exposure range.